Etching Volume Effect on the Morphology of Silicon Etched by Metal-Assisted Chemical Method

Abstract:

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Assisted by Ag nanoparticles, Si substrates were etched in aqueous solutions containing hydroﬂuoric acid (HF) and hydrogen peroxide (H2O2) with different volumes of etching solution. The etching morphology of Si wafers was found to be affected by the volumes. In etching solutions with smaller volume, the pores were created; in etching solutions with larger volume, the nanostructure composed of nanowires and nanopores (pores+wires nanostructure) were generated. In addition, the lengths of these Si nanostructures increased with the increase of the etching volume. Possible formation mechanism for this phenomenon was discussed.

Abstract: The paper reports on hydrothermal electroless etching of high resistivity p-type Si(100) at 35°C. A thin layer of platinum (Pt) was deposited onto the silicon surface by evaporation under vacuum (~ 10-6 Torr) prior to immersion in a solution of HF/Na2S2O8. The HF concentration was kept at 22.5 M while the concentration of Na2S2O8 was varied from 0.03 to 0.18 M. The etching time was varied from 15 to 75 min. The morphology and optical properties of the etched layer as a function of oxidant concentration and etching time were investigated using scanning electron microscopy (SEM) and photoluminescence measurements.

Abstract: Characterization of defect structure in silicon ribbon grown on carbon foil has been carried out. The structure of grown Si layers and a dislocation density in these layers have been studied using selective chemical etching and the Electron Backscattering Diffraction. It is observed that the layers consist of rather large grains, the majority of which is elongated along the growth direction with a similar surface orientation and with a misorientation angle between neighboring grains of 60º. This means that such grains are separated by the (111) twin boundaries. The dislocation density in different grains is found to vary from 102 to 107cm-2. The energy dispersive X-Ray microanalysis has shown that some twin boundaries are enriched with carbon.

Abstract: In this work, alkaline-based anisotropic etchants, tetramethylammonium hydroxide (TMAH) and potassium hydroxide (KOH)/isopropyl alcohol (IPA) solutions, have been used for the surface texturing of the single-crystalline silicon wafers used for solar cells. The pyramid morphology produced by the surface texturing can reduce the surface reflection of the incident light and increase the light absorption so that the efficiency of the solar cells can be increased. The experimental data shows that the optimized surface texturing has been obtained with 5 wt. % TMAH anisotropic etching at 80 °C. The surface reflectance of the polished front surface can be reduced to 17 % and the surface reflectance of the unpolished backside surface can be reduced to 3 %, respectively. This result shows that the anisotropic etching can effectively reduce the surface reflectance. While for the surface texturing with KOH/IPA mixture, the front surface reflectance can only be reduced to 35 % and the backside surface reflectance can only be reduced to 5 %, respectively. Besides, debris of Si nano-crystals exists around the pyramid base area when texturing with the KOH/IPA mixture.

Abstract: To obtain an ultralow surface reflectance and reach broadband antireflection effects,in this paper, silicon nanowires (SiNWs) layer has been fabricated by low-cost and easy-made silver-assisted etching techniques.The morphologies, reflectance and surface recombination of the samples were separately characterized. The ultralow reflectance below 3% from 300 to 800 nm under normal incidence has been realized in the case of ~ 1 μm long SiNWs whose geometry structures approximate to multi-layer gratings stack and the refractive index gradually increases from the top to the bottom of substrate. However, surface recombination of SiNWs deteriorates due to numerous dangling bonds and residual silver. Therefore, a trade-off between antireflection effect and recombination loss is the key to the electronic device.

Abstract: Due to the inertness of the intrinsic (nondoped) amorphous SiC (i-aSiC) material to the chemical impact, for making it porous by the electrochemical etching method, one must use the electrolyte solution with an appropriate composition. For this purpose we have found that besides the use of solutions containing surface activation agent (Triton X-100 for example), one can use also solutions containing oxidation agent. In this report we present the results obtained with electrolyte solution in which H2O2 plays the role of oxidation agent. Results showed that with appropriate ratio of components in the HF/H2O/H2O2 solution, we can manufacture a porous layer in the i-aSiC thin film with the porosity similar to the porosity of the porous layer obtained by etching in the HF/H2O/Triton X-100 solution with optimal composition. Thin film of i-aSiC material with porous surface layer can be used in different types of sensors.